Effects of hydrogen charge on cyclic stress-strain properties and fatigue behaviour of carbon steels

Abstract

Effects of hydrogen charge on fatigue behaviour of two carbon steels, JIS-S10C (SAE1010) and JIS-S45C (SAE1045) were investigated. There was no hydrogen effect in the cyclic stress-strain hysteresis loops of S10C hydrogen-charged with 0.2 ppm. On the other hand, the strain amplitude was decreased in S45C hydrogen-charged with 0.8 ppm. The delayed yielding and the decrease in the saturated value of the strain amplitude were observed in the hydrogen-charged specimen (H : 0.5 ppm) of S45C under the constant stress amplitude tests. It is supposed that the degree of influence of hydrogen on cyclic stress-strain properties depends or material structure and/or hydrogen content. The effect of hydrogen charge (H : 0.5 ppm) on the fatigue life, the fatigue limit and the crack growth curves of S45C were not remarkable, while there was a distinct difference in the morphology of the slip bands between the hydrogen-charged and uncharged specimens. The localized slip bands were observed in the hydrogen-charged specimen of S45C. Therefore, it is presumed that the decrease in the strain amplitude in hysteresis loop by hydrogen charge is caused by the localization of slip bands. More crack initiations from ferrite grains were observed in the hydrogen-charged specimen (H : 0.5 ppm) of S45C. This phenomenon also corresponds to the localization and the formation of slip bands.